Differential transformer with long stroke and linear output



Sept. 18, 1951 w. D. MAGGI-:ORGE 2,568,588

DIFFERENTIAL TRANsEoRMER WITH LONG STROKE AND LINEAR OUTPUT Filed June'7, 1950 ATTOR NEYS Patented Sept. 18, 1951 DIFFERENTIAL TRANSFORMERWITH LONG STROKE AND LINEAR OUTPUT William D. Macgeorge, Collegeville,Pa., assignor to Automatic Temperature Control Co., Inc., Philadelphia,Pa., a corporationA of Pennsylvania Application June '7, 1950, SerialNo. 166,659

11 Claims. (Cl. 171-119) This invention relates to differentialtransformers of the relatively movable armature type.

In application Serial Number 61,835, filed November 24, 1948, Idisclosed a novel improved differential transformer possessed of manyimportant advantages over all known prior art, of which many have beensuccessfully installed. One illustrative typical use of saiddifferential transformer is in connection with a system incorporatingtwo or more identical differential transformers, of which one is atransmitter, the relative position of the armature of which isdetermined by a prime mover, responsive to changes in condition of avariable with which it is associated. The output of the secondaries ofthe transmitter-transformer is disposed in operative relation, usuallyin series, with the output of a receiver-differential transformeridentical with the first, the position of the armature of which lattertransformer is controlled by a servo mechanism such as an electricmotor, in association with an interposed amplifier unit responsive tothe resultant phase and voltage amplitude of the secondaries circuit.With the outputs of the secondaries of the two transformers in balance,everything is at rest. With a change in condition of the variable, thearmature of the transmitter transformer isV moved to furnish atransformer-secondaries `unbalancing output which, through theamplifier, energizes the servo, the running of which actuates anindicator, recorder, or the like, or opens a valve, or performs anyother necessary or desirable work, while simultaneously moving thearmature of the receiver transformer to change the output of itssecondaries. The armature motion with the running of the servo continuesvuntil the output of the receiver transformer becomes such as tore-establisi balance in the secondaries circuit, at which point theservo stops, and the associated indicator, strip chart recorder or thelike indicates by its chan'red .indication the change in the conditionof the variable towhich the transmitter is responsive. This system isgenerally as disclosed in Hornfeck Patent No. 2,420,539.

A feature of the differential transformer disclosed in said applicationand as commercially developed thereunder is the fact that the output ofthe secondaries is linear, that is, the amplitude increases or decreasesproportionally to the movement of the armature from or relative to theposition of substantially null output or fromv tion of the particulartransformer. Furthermore, with applicants said novel transformer thislinear output is always symmetrical about the null output position. As afurther important advantage of applicants said transformer, there is thefact that the armature movement, either in unbalance from thetransmitter or in rebalance from the receiver, can develop a useablesignal with motions of the armature as small as .00004". This presentsconstituents or components of an extremely sensitive and accuratesystem, which has had excellent commercial acceptance. A transformer asdescribed, having a linear respon-se to extremely minute armaturerelative movements, is referred to hereinafter as a standard"transformer.

The improved novel standard differential trancformer as set forth insaid application replaces the previously well accepted three coildifferential transformer, namely an air cored hollow stator formed of acentral hollow air cored primary coil, with which two secondary hollowcoils were associated on opposite ends of the primary coil in end to endair spaced relation to 'F the respective ends of the primary coil andcoupled in series bucking relation, as shown in applicants earlierUnited States Patent No. 2,427,866.

An important structural feature of applicants said improved transformerof said pending application lies in the fact that it comprises twoidentical aligned hollow air cored air spaced coils, each coil formed ofidentical turns of a plurality of wires, laid on in adjacency, of whichone wire is a primary and another wire is a secondary in each coil, Aandwith the respective primary wires being identical, and the respectivesecondary wires being identical, and coupled and interconnected so as tofurnish a bucking output from the respective terminals of thesecondaries. With this novel improved coil arrangement of the standardtransformer, not only is the flux path longer than in any priortransformers, so that the linear output curve is appreciably longer, butalso the air spacing between the two coils is not critical. In contrastto this, the air spacing between the primary and the respectivesecondaries of the former three coil type is critical, and if notidentically the same lends asymmetry to the curves of the output.Moreover, the residual voltage at the null output relation of the statorand armature of the three coil system is always high, of the order of avolt or higher, whereas with applicants standard transformer theresidual voltage at the null output relation of stator and armature isof the order of perhaps one mlllivolt, due,

among other factors, to the low impedance and excellent capacitydistribution thereof as compared to the three coil transformer disclosed1n said patent, or any other known differential transformer.

Owing to the success of applicants standard transformer arrangementthere is, as noted, a rapidly growing number of installations of thetransformer systems as above discussed, and the structure of the servomotor, the amplifier and the standard receiver transformer, utilizingapplicants transformer construction has attained substantially aproduction line of commercial developments. Thus, receiver units are inproduction comprising a strip chart or other recorder, a servo foractuating the recorder, an amplifier and a receiver standarddifferential transformer actuated by the servo. These are designed foroperative assembly with transmitter units which differ as to theparticular prime mover used, according to the nature of the particularvariable to be measured or controlled, but each incorporating a standarddifferential transformer identical with that of the receiver.

The prime movers of the transmitters may be Bourdon tubes, bellows,thermostats, levers, or any other general or special prime mover.Whatever the prime mover, owing to the identity of the transformersaccording to the said application, they are arranged for incorporationin the system formed by assembly with the amplifier, servo mechanism,recorder, and standard receiver transformer. The motion of the servo hasbeen-geared down effectively to produce the slight armature motionrequired in a substantially lagless drive thereof, and the prime movermotion has' been similarly translated into related slight armaturemovements in the transmitter.

However, eillcient and important as these developments have been, theyhave heretofore been restricted in the transmitters either to primemovers having extremely slight movements, or, with devices having largermovements, to small portions of the wider movements or paths ofmovements, or to the use of some motion reduction systems which are bothexpensive and inefficient and often impart non-linear effects. So far asknown, in the case of flow meters, liquid level indicators, or, in factany devices having strokes or movements in response to the energizingchanges of conditions which are of considerable magnitude, there has notpreviously been available in the lart any transmitting device whichcould give a linearly developed signal as a function of such exaggeratedstroke along a long path capable of "matching the output of anytransformer having a minute armature movevery minute armature movements,and with which is associated' a transmitter differential transformerhaving a linear output from a null output position with exaggeratedlylong armature movements so that the linear curves match with widelydifferent armature movements; to provide a pair of differentialtransformers having the same electrical characteristics, but of whichone has an output increasing from a null output position as a functionof a minute arma- .ture movement while the other has an outputincreasing from a null output position as a function of a large armaturemovement; to provide a first differential transformer constructedaccording to the teachings of said application with each coil formed ofmultiple turns of at least two wires of known resistances and disposedin a given axial length of coil, with which is associated an armaturefor axial sliding motion relative to the two coils, and a seconddifferential transformer constructed according to the basic teachings ofsaid application with each coil formed of multiple turns of at least'twowires of known resistances and disposed in a given axial length of coilappreciably longer than the axial lengths of the coils of the firsttransformer with the number of turns and the total resistance of thewires correlated to furnish a linear output in response to a longermovement of an associated armature, with which is associated a modifiedarmature for axial sliding motion relative to said coils; to provide afirst differential transformer formed of two coils of multiple turns ofat least two wires of given axial length and known total resistancehaving a linear curve of voltage output resulting from a minute armaturemovement, and a second differential transformer formed of two coils ofmultiple turns of at least two wires of a greater axial coil length andsubstantially identical total resistance to that of the firsttransformer, having a'. linear curve of voltage output resulting from ahighly magnified movement of an armature, which respective curvessubstantially coincide; to providek two matching differentialtransformers each having a linear curve of output with relative motionsof associated armatures, of which one has a predeterminedly greaterstroke than ment, and especially none that could furnish a 1 from orrelative to the null output relation; to

provide a differential transformer with a movable element armatureoperable by movable elements of long strokes to provide a linear output;to provide a balancing system including an amplifier, a servo mechanism,and a differential transformer, with the latter having an output whichis linear from the null output position with the other in producing suchlinear curve of output; to provide a pair of matching differentialtransformers, each being formed of two air cored coils formed of twowiresv laid on in adjacency to form identical numbers of turns oflsimilar wires, of which one is of appreciably shorter axial length thanthe other, whereby linear outputs are produced by relative movements ofrespective coaxial armatures with widely divergent strokes; to providetwo differential transformers having relatively movable armatures ofwidely different respective armature strokes, but with substantiallyidentical impedances; and to provide other advantages as will becomeapparent as the description proceeds.

In the accompanying drawing forming part of this description:

Fig. 1 represents a longitudinal diametric section through the completetransformer according to the invention of said application, each coil ofwhich is formed of multiple adjacent turns of separate wires, butwithout wiring connections.

Fig. 2 represents a schematic section through the transformer accordingto the teachings of said application showing illustrative wiringconnections therefor, and the individual wires of the multiple turns,with the wires of exaggerated size and showing a. restricted number oflayers of the turns as compared with the average standard transformer,for illustrative clarity. f

Fig. 3 represents 'a schematic section through the axially elongatedtransformer of this invention, showing a modified type of ar'nature bywhich the desired linear response can be obtained.

Fig. 4 represents a schematic wiring diagram of an illustrative circuitincorporating a transmitter differential transformer according to thedisclosure of Fig. 3, and a standard receiver differental transformeraccording to the disclosure of Fig. 2, for attaining null balance of thecircuit for stopping the servomotor and moving an associated device to arelated position, lllustratively a strip chart recorder. p

Referring to the disclosure of Fig. 2, a purely illustrative embodimentof the standard transformer according to the said application is proorspool IU, comprising a cylinder having an axial bore II. and a pluralityof peripheral flanges, comprised of end ange I2, defining one end of onecoil space I4, median, preferably and aproper s ervcmotor have vbeen assmall as .0000452 Before .describingl the transformer accordingl to itsembodiment yin this invention, an illustrative complete null'balancevsystem as has vherewindings olV two vsecondaries, or shunting out someof the turns of one of the standard differential transformers,- butwhich need not be describ'edat thispoin't. In the purely illustrativecircuit of Figi, the motor M has one field yMi constantly energized by asuitable source of A. C., while the other power field Mz is selectivelyenergized by the output of theV amplifier, either of substantially novvoltage, or of a. voltage of A phase or Bphase, each substantially 90out of phase with the phase-of voltage energizing the field M1,respectivelyin one angular direcslightly larger, flange I3 defining onone surface the other end of the coil space I4 and on its other surfacedefining an end of the other coil space I5 of the transformer. The lastmentioned coll space is defined on its other end by a peripheral flangeI6. -A coll-tying and terminal connector space I1 is defined at the endof the former or spool I0 by the said flange I6 and a terminal flangeI8. The depth of the coil space is established by the outer diameter ofthe tube I0 by cylindrical surfaces 20 z In winding the transformer inthe illustrative case under discussion, two wires are laid on at one endof space I1, respectively 2| and 22, in side by side adjacency,starting, for instance, adjacent to the flange I6. Another pair of wires23 and 24 are laid on at one end of space I4, say, adjacent to theflange I3. As by rotating the spool or former I0 the wires are wound andla'd on in a multiplicity of turns, forward and back in a plurality oflayers until enough turns and layers of turns have been laid on as maybe desired for the particular desired result. To complete thetransformer, interconnections and terminal leads are connected so that,for instance, the wire 2I of completed coil 25 is conv-nected in serieswith wire 23 of completed coil 26, to form the primary winding for thetransformer. and wire 22 of coil 25 at its end adjacent to the flange I3is connected to the wire 24 of coil 26 at its end adjacent to the'flangeI2, to couple the secondary windings in series bucking relation, havingoutput leads 21 and 28. The primary input connections Il) and 3| areconnected to the respective ends of the series-connected primarywindings. To complete the transformer an armature mass of magnetizablematerial as indicated at 32 is mounted for axial sliding in the bore II.Th s is preferably of the same axial length as the total combinedlengths of the coils 25 and 26, plus the spacing flange I3.

The illustrative standard transformer as thus described when energizedby A. C. in the exciting coil has a linear curve of voltage output,which is symmetrical about the null output position of the armaturerelative to the stator. The increments of armature movement to securethe linear output and a useable signal on this curve are quite minuteand with suitable amplification tion or the other relative Ato the phaseof the voltage in M1, so tha-t the motor M runs selectively in onedirection organother, or stops. as

will be clear. vThe servomotor'M, in its running, actuates any suitableelement of a recorder, such as the scribing point 50, operativetransversely relative to a strip chart 5I, moved at a timed rateby asecond motor MR. y

A receiver differential transformer R. D. T. is provided which isusually the said standard transformer, having primaries 60 and 6I andsecondariess'and 49, with mutual interconnections so that the outputs ofthe secondaries are respectively Imutually bucking, as taught in saidcopendirigfapplication. Forfsimplicity, but not necessarily,ltheAprimaries are shown as seriesaiding relation, andthesecondaries areVshown as series bucking relation. The output of the secondaries iscontrolled by the positioning of the armature 32 which is axiallymovable and positionable in the stator formed of the said primaryandrsecondarycoils, by a, suitable link or like l vconnection to themotor M.r Y As the motor M runs in one direction or the otherpredetermined increments of armature Aposition change attach to thearmature for 1a given predetermined number of rotations of the motor MwA transmitter' discrtion-"transformer T. D. T;

l is provided, which may-be and in the prior artis a "standarddifferential-transformer, but which in the present instancev comprisesthe improved impedance matching transformer of this invention, to bedescribed. The transmitter trans- 0 differentially wound secondaries ofa fixed transformer, if a range change is to be incorporated in thesystem. The outputs of the secondaries of the transformers T. D. T. andR. D. T. are series connected through the primary of a fixed transformerT, the secondary of which feeds an amin a rotometer or a liquid levelindicator or the like, indicated generally at 63.

With everything in balance, the scriber 50 is at a given positionrelative to the strip chart I, coinciding with a given position ofarmature 62 of the transmitter T. D. T. as a function of the conditionof the variable, and the motor M is stationary. With movement of thearmature 62 of the transmitter transformer T. D. T. the output of thesecondaries 56 and 51 changes and unbalances the outputs of thesecondaries 60 and 6| ofthe receiver transformer R. D. T., which,through transformer T and the amplifier places a voltage of given phaseon the power winding M2 of the motor M, and the motor runs in the properdirection and to a degree such that the armature 32 is repositioned inthe transformer R. D. T. to change the outputs of its secondaries 60 and6l until it re-establishes balance with the previously changed output ofthe secondaries of transformer T. D. T., until the outputs of thesecondaries are again in balance, when the motor stops.' Meanwhile, thescriber 50 has moved relative,v to the chart 5l until the change of itssetting corresponds with the change in the prime mover 63 which actuatedthe armature 62 of the transformer T. D. T. With standard differentialtransformers having complete electrical identity, the linear output ofboth transformers conduces toward extremely accurate balance andaccurate measurements and recordations of the disturbance or temporaryunbalance.

In order to furnish an illustration of the dimensions and proportions ofthe standard differential transformer, in a purely illustrativeembodiment thereof, as a background for the improved transformer of thisinvention, let it be assumed that the coils of the standard transformerareeach formed of two wires laid on in adjacency in multiple layers,that there are 400 turns of each wire in each coil, that the finishedcoils are 1A; of an inch in thickness with an internal diameter of 1/2inch, and that each coil is of an inch long,

vthe illustrative wire used is enameled wire of f y.0088" in diameter,and the resistance of the respective wires measured overthe 400 turns isi known. To form apmatching elongated transas the diameter of the spool.The spool 10 having an internal bore 69 with an external diameter thenof of an inch, is formed with shallow end flanges 1I and 12, each spacedfrom a wider central shallow flange 1,3. by an illustrative Vseveninches of coil area, respectively 14 and 15, so that the operatinglength of the elongated transi l.renner of this invention is 14 inchesp1us the widthof the central flange area, which is of the order Vo1.' 1and V; inches. Upon the same ends of the respective coil areas, forinstance. at the left hand thereof adjacent to the respective flangesbounding those ends of the areas 'Il and 16, two wires, respectively 2|'and 22', and 28' and 24'. illustratively, preferably identicalrespectively with wires 2|, 22, 23, and 24, are laid on in adjacency,and the spool is turned to dispose the wires in elongatetd coil formlining the coil area spaces 'Il and 'l5 with respective coils 25' and26', but, of course. in a sharply reduced number of layers of turns,which in the illustrative case is formed of a single layer, of closelycontiguous turns of the respective wires.. The respective wires of theprimary and secondary windings are interconnected as in the case of thestandard transformer with which they are to be associated so that the'secondary leads have bucking outputs. Owing to the elongated nature ofthe novel transformer as thus constructed, a modified form of axiallymounted and movable armature 62 is provided. This provides the structureof transmitter transformer T. D. T.

In the illustrative case, the modified armature 62 comprises fourarmatures of the same general formation and size as the armature 32 ofthe receiver transformer R. D. T. To secure the proper alignment of thecomponents of the armature, an aluminum or other rod or stiff wire ofnonmagnetic properties 86 is provided upon which armature components 8|and 82 are stryng and fastened separated by a non-magnetic spacingwasher or the like 83, of illustratively 1% of an inch axial length witharmature 83 spaced by three of such spacing washers 84, 85, and 86, fromthe adjacent end of an armature component Il, spaced by a single washer8l from`the terminal armature component 90. While with suitable care asingle elongated integral armature may be constructed, it is found thatthe elongated compound armature gives eilicient and satisfactoryresults, while simplifying the construction by providing simplemultiples of the same armatures as are used with the said standardtransformers.

While the improved elongated transformer as thus described is adequateto furnish a ve inch stroke of the armature 62 in providing the linearmatching output of the small standard transformer as described, it willbe understood that in translating the turns of the standard transformerinto the elongated transformer, it happens with the particular gauge-ofwire referred to, to dispose all of the turns in side by side laterallycontacting relation in a single layer. If greater elongation oftransformer and the stroke of the armature is required, the turns ofindividual wires are laid on the elongated former respectively in islightly or greatly spaced relation so that there is no side by sidecontact of the adjacent wires. On the other hand, for a shorter armaturestroke for the given output it will be seen that the turns can beapplied in side by side adjacency in more than one layer in a shorterelongated spool area. still greater than the standard, and still furnishthe linear output desired, so long as the impedances aresubstantiallyidentical.

While in securing the desired result it is simpler and `easier to usethe same gauge of wire with the same resistances, in both the standardand the elongated armature, and to provide a sligh.ly greater diameterof the external spool surface than is used on the standard transformer,neither Aof these factors is limiting, as the only essential is that thetwo transformershave identical or substantially identical impedances.

Thus, using the system of the transformer of said application it will beseen that it is not essential spool 80.

that the number of turns of the respective wires on the related coils besimilar. The wires may be of different diameters and therefore ofdifferent resistance, and the difference in respective resistances maybe compensated by having a suitable differential between the number ofturns on the respective coils of the respective matching transformers.The problem in matching the outputs of the transformers having small andlarge strokes respectively is the phase shift control which isaccomplished by the presence of identical impedance in bothtransformers.

It is contemplated that the elongated transformer armature or core 62may be associated with a tubular housing undervpressure to comprise ofitself a float. Thus. a cylindrical tube of non-magnetic material, suchas of brass, nonmagnetic stainless steel or the like, encloses thearmature components and may be closed at both ends and filled with gasso as of itself to cornprise a float, or it may be sealed and mounted ona float. In any case. it protects the armature components againstliquids which might attack the magnetizable material of the components.Such a non-magnetic housing is shown at |00. In order to protect thestator mounting from such liquid. it may be found desirable to insert asleeve Ill of similar non-magnetic material axially through and evenbeyond the ends of the This furnishes in this instance two thin layersof non-magnetic material in juxtaposition inside of the bore 69 of theelongated stator. This eilects a phase shifting of the output of thesecondaries of the elongated transformer affecting its matching with theoutput of the standard transformer. It is part of this invention tocorrect for this phase shifting phenomena in the standard transformer R.D. T. by simply inserting a brass or like non-magnetic sleeve |02 intothe bore of the stator, within which the armature 53 moves. lThis shorttube of the length of transformer R. D. T. and of the same generalthickness as the two elongated tubes l" and I I of T. D. T. or ofeither, if but one is used, corrects the phase shift and causes theoutputs of the two transformers to be exact sensitive accurateduplicates of each other, but with the widely different lengths ofarmature strokes or movements.

Having thus described my invention, I claim:

1. A differential transformer comprising a first and a second air coredcoil in axial alignment and juxtaposed relation in a non-magneticassembly,

the first coil being formed of at least a first and a second wire, andthe second coil being formed of at least a third and fourth wire, ofwhich the first and third are identical and said second and fourth areidentical, the respective coils each comprising identicalmultiple turnsof their respective wires laid on in adjacency so that the coils areidentical, with said first and second wires and said third and fourthwires respectively in mutual inductive relation throughout the lengthsof their said respective coils, means interconnecting the rst and thirdwires to form a transformer primary having connections for an energizingA. C. input, means interconnecting said second and fourth wires to forma transformer secondary having output connections connectively isolatedfrom the transformer primary, and a magnetic core disposed for axialadjustment in and relative to the two aligned coils, the saidinterconnections establishing the output of the transformer secondary asa resultant of opposing voltages whereby with the core substantiallymedially disposed in the coils the secondary output is substantiallynull becoming a voltage of one phase or the opposing phase as the corerelatively moves from the medial disposition in one direction or theother increasing in amplitude as a linear function of movement from themedial position, said linear change in amplitude being symmetrical onboth sides of said substantially null output, said core comprised of aplurality of substantially cylindrical individual core elements inaxially aligned air spaced relation, and means mounting the coreelements for movement as a unit axially of said axially aligned coils.

2. A differential transformer as recited in claim l, in which both coilsare elongated to an extent adequate to receive and substantially housethe` plurality of aligned core elements in the null output relationthereof to the coils, and in which the coils are formed of multipleturns in appreciably less than a multiplicity of layers in effectingsuch elongation.

3. A differential transformer as recited in claim l, in which both coilsare elongated to an extent adequate to receive and substantially housethe plurality of aligned core elements in the null output relationthereof to the coils, and in which the coils are formed of multipleturns in a single layer in effecting such elongation.

4. A differential transformer comprising a first and a second air coredcoil in axial alignment and juxtaposed relation in a non-magneticassembly, the rst coil being formed of at least a rst and a second wire,and the second coil being formed of at least a third and a fourth wire,of which the first and third are identical and said second and fourthare identical, the respective coils each comprising identical multipleturns of their respective wires laid on in adjacency so that the l coilsare identical, with said first and second wires and said third andfourth wires respectively in mutual inductive relation throughout thelengths of their said respective coils, means interconnecting the firstand third wires to form a transformer primary having connections for anenergizing A.C. input, means interconnecting said second and fourthwires to form a transformer secondary having output connectionsconnectively isolated from the transformer primary, and a magnetic coredisposed for axial adjustment in and relative to the two aligned coils,the said interconnections establishing the output of the transformersecondary as a vresultant of opposing voltages whereby with the coresubstantially medially disposed in the coils the secondary output issubstantially null becoming a voltage of one phase or the opposing phaseas the core relatively moves from the medial disposition in onedirection or -the other increasing in amplitude as a linear function ofmovement from the medical position, said linear change in amplitudebeing symmetrica] on both sides of said substantially null f output,said core comprised of a plurality of substantially cylindricalindividual core elements in 11 turns in a predetermined axial length,means interconnecting selected wires of the coils to form a primary anda secondary, the output leads oi which latter have respectively mutuallybucking outputs, and an armature core in axially movablel relation toboth coils to furnish a substantially null output or an output ofvoltagel of selected phase and linearly changing amplitude proportionalto relative movements of the armature relative to its null outputrelative position with small increments of relative armature movements,said second transformer comprising two identical air cored coils inaxial alignment and air spacing each comprised of at least two wireslaid on in adjacency in substantially the same number of turns as and inan axial length appreciably greater than that of the coils of the saidfirst transformer, means interconnecting selected wires of the coils ofthe second transformer to form a primary and a secondary the outputleads of which latter have respectively mutually bucking outputs, and anarmature core of appreciably greater length than the said armature coreof said rst transformer axially movable relative to both coils tofurnish a substantially null output or an output of voltage of selectedphase and linearly changing amplitude proportional to relative movementsof the second armature from its substantially null output position withlonger increments of relative motion, means in the system for moving thearmature core of the first trans- I former through small motions tosecure a linear change of output from its said secondary, and means inthe system for moving the armature core of the second transformerthrough larger motions to secure a linear change of output from itssecondary equivalent in amplitude to the change in secondary output ofsaid first transformer with small motions.

6. A differential transformer system comprising a first and a seconddifferential transformer, each transformer comprising respectively twoidentical air cored coils in axial alignment and air spacing and eachcomprising at least two wires laid on in adjacency in multiple turns ina given axial length, means interconnecting selected wires of therespective coils of the respective transformers to form a primary and asecondary the output leads of which latter have respectively mutuallybucking outputs, an armature core in axially movable relation to bothcoils of the respective transformers to furnish a substantially nulloutput or an output of voltage of selected phase and linearly changingamplitude proportional to relative movements of the respective armaturesrelative to its null output relative position in the coils of therespective transformers, both transformers having substantiallyidentical impedance but the given axial lengths thereof being widelydifferent in the said two transformers, so that matching linear outputsfrom the transformers follows from widely different increments ofarmature movement in the respective transformers and means in the systemfor securing differential relative motions of the respective armaturesand the respective aligned coils to secure `identical outputs from therespective secondaries of the respective transformers.

A7. A differential transformer system comprising a first and a seconddifferential transformer, each transformer comprising respectively twoidentical air cored coils in axial alignment and air spacing and eachcomprising at least two lected wires of the respective coils of therespective transformers to form a primary and a secondary the outputleads of which latter have respectively mutually bucking outputs, anarmature core in axially movable relation to both coils of therespective transformers to furnish a substantially null output or anoutput of voltage of selected phase and linearly changing amplitudeproportional to relative movements of the respective armatures relativeto its null output relative position in the coils of the respectivetransformers, both transformers having substantially identical impedancebut the given axial lengths thereof being widely different in the saidtwo transformers, so that matching linear outputs from the transformersfollows from widely different increments of armature movement in therespective transformers and means in the system for securingdifferential relative motions of the respective armatures and therespective aligned coils to secure identical outputs from the respectivesecondaries of the respective transformers,

the armature associated withthe coils of greater axial length havingappreciably greater length axially than the armature of the other ofsaid transformers.

8. A differential transformer system comprising a first and a seconddifferential transformer, each transformer comprising respectively twoidentical air cored coils in axial alignment and air spacing and eachcomprising at least two 'wires laid on in adjacency in multiple turns ina given axial length, means interconnecting selected wires of therespective coils of the respective transformers to form a primary and asecondary the output leads of which latter have respectively mutuallybucking outputs, an armature core in axially movable relation to bothcoils of the respective transformers to furnish a substantially nulloutput or an output of voltage of selected phase and linearly changingamplitude proportional to relative movements of the respective armaturesrelative to its null output relative position in the coils of therespective transformers, both transformers having substantiallyidentical impedance but the given axial lengths thereof being widelydifferent in the said two transformers, so that matching linear outputsfrom the transformers follows from widely different increments ofarmature movement in the respective transformers, said `systemcomprising circuit means combining the outputs of the respectivetransformers in a signal relationship, means for relativelymoving thearmature of the axially shorter transformer with short increments ofmovement, and means for moving the armature i of the longer transformerwith longer increments to produce balanced signal relationship.

9. A differential transformer system comprising a first and a seconddifferential transformer. each transformer comprising two identical aircored coils in axial alignment and air spacing, and'each comprising atleast two wires laid on in adjacency and multiple turns in givenrespectively diiferent axial lengths, means interconnecting selectedwires of the respective coils of the respective transformers to form aprimary and a secondary out of conductive interconnection, and theoutput leads of which secondaries have respectively mutually buckingoutputs, armature cores of respectively different lengths disposed inaxially movable relation to both coils of the respective transformers tofurnish a substantially null output or an output of given phase andlinearly changing amplitude proportional to relal tive movements of therespective armatures relaaccesso 13 tive to its null output relativeposition in the coils of the respective transformers, the longer of thesaid armatures being mounted for motion in the transformer from thecoils of greater axial length,

the impedances of the respective transformersA being substantiallyidentical so that the linear outputs are of identical phase relationsand arise from widely different axial movements of the respectivearmatures, with the longer armature having a longer stroke in itstransformer for the linear output than the armature of the other of saidtransformers means in the system for relatively moving the armature ofthe axially shorter transformer through a relatively small motion toproduce a change from null output to a linearly developed maximumamplitude of output, and means in the system for relatively moving thelonger armature of the axially longer transformer through a relativelylarge motion to produce a change from null output to a linearlydeveloped maximum amplitude of output the equivalent of the maximumoutput of said axially shorter transformer.

10. A differential transformer system comprising a first and a seconddifferential transformer, each comprising two identical air cored coilsin axial alignment and air'spacing, the first coil being formed of atleast a first and a second wire, and the second coil being formed of atleast a third and a fourth wire, of which the first and third areidentical in all coils, and of which the second and fourth are identicalin all coils, the respective coils each comprising identical multipleturns of their respective Wires laid on in adjacency so that the coilsare electrically substantially identical with said first and secondwires and said third and fourth wires respectively in mutual inductiverelation throughout the lengths of their said respective coils, but withthe coils of the first transformer in multiple layers in a given axiallength with a given internal diameter and the coils of the secondtransformer in a fewer number of layers and in an appreciably greateraxial length on a slightly greater internal diameter than the coils ofthe first transformer, means interconnecting said first and third wiresof the respective transformers to form primaries having connections foran energizing A. C. input, 'means interconnecting said second and fourthwires of the respective transformers to form secondaries having outputconnections and connectively isolated from the primaries of therespectiva transformers, and first and second magnetic cores ofappreciably different axial lengths disposed respectively for axialadjustment in and relative to the respective aligned coils of the firstand second transformer, the said interconnections establishing theoutputs of the secondaries of the respective transformers as a re-lsultant of opposing voltages varying from a substantially null output toan output of one phase or an opposing phase as the core moves relativeto a position of substantially null output increasing in amplitude as alinear function of movement relative to said position of substantiallynull output, the increments of core movement for a given voltage outputbeing widely different in the respective transformers, and means in thesystem for imparting' the respective increments to the respectivearmatures of the respective transformers to furnish equivalent voltageoutputs into the system from said respective transformers.

1l. A differential transformer system comprising a first and a seconddifferential transformer, one of which has a relatively small range ofmovement of the relatively movable element thereof for producing anoutput progressing in a substantially linear curve from a substantiallynull output to a signal of given amplitude, said other transformerhaving a relatively large range of movement of the relatively movableelement thereof for producing an output progressing in a substantiallylinear curve from a substantially null output to a signal of the samesaid given amplitude, means coupling said transformers in a balancingnetwork, a first actuating means having a relatively short strokecoupled to the relatively movable element of the transformer having therelatively short stroke, a second actuating means having a relativelylong stroke coupled to the relatively movable element of the transformerhaving the relatively long stroke, movable means in the network movableas a function of unbalance of signals between the transformers andstopping when balance is attained, one of said actuating means beingresponsive to changes in the condition of a variable and the other beingresponsive to movement of the movable means,

y whereby network signal unbalance caused by changed output from onetransformer is rebalanced by the complemental change of output from theother transformer with a differential between the lengths of theunbalancing and rebalancing respective strokes.

WILLIAM D. MACGEOR/GE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,315,609 Fielder Apr. 8, 19432,420,539 Hornfeck May 13. 1947 2,437,603 Hornfeck Mar. 9, 19482,450,868 Berman Oct. 12, 1948 FOREIGN PATENTS Number Country Date581,065 France May 2, 1924

